Combine the oil and the mustard seeds in a large wok or frying pan over medium-high heat. Cover (the mustard seeds pop and splatter) and cook until you hear the mustard seeds crackle, 1-2 minutes.

Add the cumin seeds, turmeric, dried and fresh chilies, and curry leaves, and the asafetida and coconut if using. (Stand back—the curry leaves spit when they hit the oil.) Turn the heat down to low and cook uncovered, stirring, until the coconut begins to turn golden brown, about 1 minute.

Add the squash and turn the heat back up to medium-high. Stir to coat the squash with the spices. Then cook, stirring often, for 5 minutes.

Add the salt and cook, stirring, until the squash is tender but still has some bite, 3-4 minutes longer. Taste for salt and serve hot.